(a) Field of the Invention
The present invention relates to a plasma display device and a driving method thereof.
(b) Description of the Related Art
Development of flat panel displays, such as liquid crystal displays (LCD), field emission displays (FED), and plasma display panels (PDP), has been actively pursued in the recent years. The PDP is advantageous over other flat panel displays due to its high luminance, high luminous efficiency, and wide viewing angle. Accordingly, the PDP is in the spotlight as a substitute for the conventional cathode ray tube (CRT) for large-screen displays of more than 40 inches.
The PDP may be an AC PDP or a DC PDP based on the method used for driving the PDP. The DC PDP has electrodes exposed to a discharge space, thereby causing current to directly flow through the discharge space during application of a voltage to the DC PDP. In this regard, the DC PDP has a disadvantage in that it requires a resistor for limiting the current. On the other hand, the AC PDP has electrodes covered with a dielectric layer that naturally forms a capacitance component to limit the current and protect the electrodes from the impact of ions during discharge. As a result, the AC PDP lasts longer than the DC PDP.
The PDP is driven during frames of time One frame of the AC PDP is divided into a plurality of subfields each having a respective weight. Each subfield includes a reset period, an address period, and a sustain period.
The reset period is for initializing the status of each discharge cell to facilitate an addressing operation on the discharge cell. The address period is for selecting turn-on/turn-off cells (i.e., cells to be turned on or off) and accumulating wall charges in the turn-on cells (i.e., addressed cells). The sustain period is for sustaining a discharge in the addressed cells for displaying an image.
FIG. 1 is a driving waveform diagram of a conventional plasma display device. During the sustain period, a voltage Vs is alternately applied to a scan electrode Y and a sustain electrode X while an address electrode A is biased with a reference voltage (0V in FIG. 1).
During the sustain period, the voltage Vs is applied to the scan electrode Y and a sustain discharge is generated between the scan electrode Y and the sustain electrode X. Accordingly, negative (−) wall charges and positive (+) wall charges are respectively formed on the scan electrode Y and the sustain electrode X. However, when the sustain discharge is generated, the positive (+) wall charges are distributed to the sustain electrode X as well as the address electrode A. Accordingly, the amount of positive (+) wall charges formed on the sustain electrode X will not be sufficiently large to generate a next sustain discharge that is adequate, thereby causing a decrease of luminous efficiency.
Various studies have been conducted in order to improve the luminous efficiency. In one study, a discharge gap of approximately 60 μm to 120 μm (hereinafter referred to as a “short discharge gap”) is formed between a scan electrode and a sustain electrode located within one discharge cell. The discharge cell structure in which the aforementioned short discharge gap is generated has limitations that prevent significant improvement of luminous efficiency. To overcome these limitations, a new discharge cell structure and accordingly a new driving method have been considered. For example, a technology using positive column discharge characteristics has been researched. According to the technology, a discharge gap of 400 μm or greater in size (a so-called “long discharge gap”) is formed between the scan electrode and the sustain electrode located within one discharge cell, and a positive column discharge is generated in the long discharge gap. However, there is a problem in that a discharge firing voltage and a sustain discharge voltage (Vs) are increased in order to generate the positive column discharge for improving luminous efficiency.